I have an album with album artist "Various Artists" (but that isn't significant to the observation) and songs have 1 or more artists assigned.

This concerns songs with more than 1 artist. What I found is that if there is one song artist and also MUSICBRAINZ_ARTISTID for that artist will scan properly. Now if there is more than one song artist, and still a single MUSICBRAINZ_ARTISTID only the first artist will be scanned. The second and further are ignored.

So I then tested but this time I included MUSICBRAINZ_ARTISTID for all artists on the song. This time I did get all artists scanned, but it would only use the first artist name (repeated as many times as there are MUSICBRAINZ_ARTISTID tags) unless the "override tag" setting is used. Then it showed all artists (for which MUSICBRAINZ_ARTISTID is provided). Again if there are 3 artists and 2 MUSICBRAINZ_ARTISTID you only get two artists scanned.

ISTM that if there are more song artists than MUSICBRAINZ_ARTISTID tags that all artists from the Artist tag(s) should be scanned to the database. Obviously there is a problem of relating the Artist tag to the MUSICBRAINZ_ARTISTID tag (could be by order in the file but I can see that's problematic).

In this test the musicinfo scanner finds the file, scans the album using MUSICBRAINZ_ALBUMID and uses Universal Album Scraper to get album data. Next it scans the album artist data using "Various Artists" and uses Universal Artist Scraper to get artist data. Next is runs the music info scanner using the MUSICBRAINZ_ARTISTID (Christina Aguilera) and uses Universal Artist Scraper to get artist data. The musicinfo scanner then terminates without adding or finding the three other artists (Lil’ Kim, Mýa & P!nk).